According to the multilevel interconnect structure of a semiconductor device, the aspect ratio (the ratio of depth to width) of a contact or via hole generally continues to increase since a proportionate decrease in the contact or via hole depth is typically not realized with the decrease in the width of the contact or via hole. Accordingly, a conventional method for fabricating a metal interconnection layer has limitations, such as non-planarity, poor step-coverage, metal shorts, low yield and degraded reliability. To overcome these problems, a new interconnect technology called Dual Damascene process in which a contact plug and a metal interconnection layer are simultaneously formed, has been suggested.
FIGS. 1 through 4 are sectional views for explaining a method for forming a metal interconnection layer of a semiconductor device using a conventional Dual Damascene process.
Referring to FIG. 1, an insulating later 12 is formed on a semiconductor substrate 10. Subsequently, a lower metal layer 14 is formed on the insulating layer 12 and then a dielectric layer 16 is formed on the lower metal layer 14.
Referring to FIG. 2, the dielectric layer 16 is etched to form a contact hole 17 partially exposing the lower metal layer 14. Then, a barrier metal layer 18 is formed over the resultant structure. The barrier metal layer 18 may be formed of a titanium (Ti) film and a titanium nitride (tin) film.
Referring to FIG. 3, a metal layer 20 is formed of tungsten on the resultant structure having the barrier metal layer 18 formed therein by a chemical vapor deposition (CVD) method. Generally, the metal layer 20 formed by the CVD method must be formed of a material having a low resistance and excellent step coverage. If the metal layer 20 is not effectively buried in the contact hole 17, the contact resistance is increased.
Referring to FIG. 4, the metal layer 20 on the dielectric layer 16 is polished by a chemical mechanical polishing method to form a metal plug 22 buried in the contact hole 17 as a metal interconnection layer.
However, according to the method for forming the metal interconnection layer using the aforementioned conventional Dual Damascene process, since the metal layer 20 and a metal plug 22 are formed of the same material, the metal material for forming the metal layer 20 is restricted to a material having an excellent capability of burying the contact hole.